The growing demand for mobile and portable telephone services has led to the creation of new standards for cellular phones. These standards, such as the European digital standard (GSM), the United States Digital Cellular (USDC) in North America and the Japanese Personal Digital Cellular (PDC) incorporate digital voice and Time Division Multiple Access (TDMA) protocols that enable a substantial increase in capacity, compared to the existing analog systems.
The standards are typically implemented in both hardware and software, wherein the software operates on a digital signal processing (DSP) chip and the hardware operates on a few application specific integrated circuit (ASIC) chips. On the transmitting end, the software typically compresses the speech signals received from a coder/decoder (CODEC) and the hardware prepares the compressed speech signals for transmission, adding error correction codes and control channel signals to the compressed speech signals and then modulating the resultant signal. On the receiving end, the hardware demodulates the received signals and processes them into compressed speech signals and control channel signals. The software then decompresses the speech signals and provides them to the CODEC.